Well Stock Car Extreme has some hillclimbs like Transfagarasan which is long or
Montenegro - GlavaZete which is short but there are some others. It probably needs a permissions but if they have it for GSCE, FTruck shouldn't be problem.

So I have tried it and must say trucks probably can't pass that rally stage. The best and maybe the only one hillclimb they fit for sure is Transfagarasan. And maybe Pikes Peak. But they are very long.